1. Field of the Invention
The present invention relates to a novel retinol derivative and a cosmetic composition comprising the same, in particular, to a novel retinol derivative exhibiting the effects from both L-ascorbic acid and retinol as well as being free from the disadvantages of two compounds such as skin irritation and instability in cosmetic formulation, and a cosmetic composition comprising the retinol derivative.
2. Description of the Related Art
Various reasons may lead to skin spots such as freckles. The main reason is ultraviolet radiation. When skin is exposed to ultraviolet ray, melanin is generated in melanocytes and released and deposited on epidermis, resulting in formation of skin spots such as freckles. In the process of melanin generation in melanocytes, tyrosinase catalyzes the formation of DOPAquinone using tyrosine as substrate and then DOPAquinone undergoes spontaneous reaction and enzyme reaction to generate a copolymeric black pigment, melanin. Thus, to maintain a clear and fair skin, it is necessary to inhibit melanin biosynthesis in melanocytes and the deposition of melanin on skin.
L-ascorbic acid (Vitamin C) exerts good antioxidizing property, inhibition of melanin biosynthesis in melanocytes and enhancement of collagen biosynthesis in fibroblast, so that it is generally used as active ingredient in cosmetics for whitening skin color or eliminating wrinkle. However, L-ascorbic acid has a limitation as cosmetic material due to instability in cosmetic formulation. In order to overcome such disadvantage, several derivatives, which include AA-2P (L-ascorbic acid 2-phosphate), AA-2S (L-ascorbic acid 2-sulfate), AA-6G (6-O-α-D-glucopyranosyl-L-ascorbic acid) and AA-2G (2-O-α-D-glucopyranosyl-L-ascorbic acid), have been developed and employed in place of L-ascorbic acid as cosmetic ingredient.
Skin aging is ascribed to intrinsic aging and photo aging and the latter is believed to a main factor for skin aging. Photo aging is likely to be a cumulative result of the changes occurring in skin such as wrinkles, thickening, flaccidity, decreased elasticity, roughness, dryness and spots, which are attributed to aging by sunlight, in particular, ultraviolet. In other words, skin aging by sunlight may cause the changes in epidermis and dermis, thereby giving rise to wrinkles, thickening and decreased elasticity of skin.
Retinol (Vitamin A) has been well known as cosmetic material for treating and preventing skin aging (U.S. Pat. Nos. 4,603,146 and 4,877,805). Retinoid useful for skin caring includes retinol (vitamin A alcohol), retinal (vitamin A aldehyde) and retinyl acetate, retinyl propionate, retinyl linoleate and retinyl palmitate as retinyl esters. Among them, retinol found in human cell is pivotal in differentiation and growth of epithelial tissue and exhibits higher stability than other retinoids, which enable popular employment of retinol as cosmetic material. However, retinol having the superior effects in treatment and prevention of wrinkle and acne has some disadvantages: (a) as formulated, the changes of color and odor and the reduced efficacy; and (b) skin irritation while low level of retinol is used. Therefore, the use of retinol as cosmetic material has been highly limited.